1. Field of the Invention
The present invention relates to coding a TFCI (Transport Format Combination Indicator) for mobile communications, and more particularly, to TFCI code word mapping in a hard split mode.
2. Background of the Related Art
Wideband Code Division Multiple Access (W-CDMA) defines a channel structure by which various data services can be effectively provided to a plurality of users. According to W-CDMA standards, the data to be transmitted to each terminal (e.g., a mobile station) are processed by one or more transport channels (TrCH) based on commands from higher layers. Further, the data of a transport channel are mapped to one or more physical channels that are allocated to the terminals.
In more detail, the data generated at higher layers is carried over the air with transport channels, which are mapped in the physical layer to different physical channels. In addition, each transport channel is accompanied by a Transport Format Indicator (TFI) for each time event at which data is expected to arrive from the higher layers for a specific transport channel. The physical layer combines the TFI information from different transport channels into a Transport Format Combination Indicator (TFCI). The TFCI is coded and transmitted over the physical control channel to inform the receiver about the transport channels that are active for the current frame. In one example, the TFCI has a length of 10 bits and is encoded into 32 bits to be transmitted over the physical channel.
In addition, a transport channel is defined by the particular characteristics of the data to be transmitted and by the particular manner in which the data is transmitted over an air interface using a service provided to the higher layer by the physical layer. The transport channels are classified into dedicated transport channels and common transport channels. Only one type of dedicated transport channel exists, namely, a dedicated channel DCH). In contrast, there are six types of common transport channels, namely a broadcast channel (BCH), a forward access channel (FACH), a paging channel (PCH), a random access channel (RACH), a common packet channel (CPCH), and a downlink shared channel (DSCH).
The DSCH is a downlink transport channel that is shared by a plurality of terminals, and is associated with one or more downlink DCHs. Further, the DSCH is transmitted to an entire cell, or is transmitted to a portion of a cell if beam-forming antennas are used.
As the DSCH and DCH are related to each other, transmission from the base station to the terminal via the DSCH is possible. Thus, each terminal that can transmit on the DSCH has an associated single dedicated physical channel (DPCH). The associated DPCH is used for transmitting control commands for the associated uplink DPCH, if necessary.
Currently, there are two types of methods for coding the information related to the DCH and the DSCH. The first method is called a logical split mode in which a code word is formed using second order Reed-Muller coding for the TFCI information (TFCI1) of the DCH and the TFCI information (TFCI2) of the DSCH. The second method is called a hard split mode in which the TFCI information of the DCH and the TFCI information of the TFCI of the DSCH are separately coded into code words, and the bits of these two code words are mixed and then transmitted.
In other words, for the logical split mode, a 5-bit TFCI1 (which is a TFCI for the DPCH (Dedicated Physical Channel)) is encoded together with a 5-bit TFCI2 (which is a TFCI for the DSCH (Downlink Shared Channel)) and transmitted over the DPCCH (Dedicated Physical Control Channel). In contrast, for the hard split mode, the TFCI1 and TFCI2 are encoded separately and transmitted over the DPCCH. Namely, in one example, a (32,6) second order Reed-Muller code is used for the logical split mode, while a (16,5) first order Reed-Muller code is used for the hard split mode.
Further, other various TFCI1 to TFCI2 ratio combinations (e.g., 3:7, 4:6, 6:4, 7:3) are used. For example, if 10 input information bits (i.e., TFCI bits) are divided in a 1:9 ratio, then 30 coded output symbols (i.e., forming a TFCI code word) are divided in a 3:27 ratio. That is, although a total of 32 coded bits are output based on the inputted information bits, the last two transport combination information bits are not transmitted due to a limitation in the total number of the TFCI fields that are actually transmitted. In other examples, if the 10 input information bits are divided in a 2:8 ratio, then the 30 coded output symbols are divided in a 6:24 ratio; if the 10 input information bits are divided in a 3:7 ratio, then the 30 coded output symbols are divided in a 9:21 ratio; and if the 10 input information bits are divided in a 4:6 ratio, then the 30 coded output symbols are divided in a 12:18 ratio.
Currently, the bit positions j1 (=bit positions for the TFCI1 bits) and j2 (=bit positions for the TFCI2 bits) are obtained by the following Equations 1a through 1d:
                                                        If              ⁢                                                          ⁢              k                        ≠            5                    ,                                          ⁢                                          ⁢                                    j              1                        =                                          ⌊                                                                            32                                                                        3                          ×                                                      min                            ⁡                                                          (                                                              k                                ,                                                                  10                                  -                                  k                                                                                            )                                                                                                      +                        1                                                              ×                                          (                                                                        i                          1                                                +                        1                                            )                                                        +                                      1                    2                                                  ⌋                            -              1                                      ⁢                                                      (                  1          ⁢          a                )                                                                    If              ⁢                                                          ⁢              k                        =            5                    ,                                          ⁢                                          ⁢                                          ⁢                                    j              2                        =                                          i                2                            +                              ⌊                                                                                                    32                        ×                        min                        ⁢                                                                                                  ⁢                                                  (                                                      k                            ,                                                          10                              -                              k                                                                                )                                                                    +                      1                                                              32                      -                                              (                                                                              3                            ×                                                          min                              ⁡                                                              (                                                                  k                                  ,                                                                      10                                    -                                    k                                                                                                  )                                                                                                              +                          1                                                )                                                                              ×                                      (                                                                  i                        2                                            +                                              1                        2                                                              )                                                  ⌋                                                    ⁢                                                      (                  1          ⁢          b                )                                                      j            1                    =                      2            ×                          i              1                                      ⁢                                                      (                  1          ⁢          c                )                                                      j            2                    =                                    2              ×                              i                2                                      +            1                          ⁢                                                      (                  1          ⁢          d                )            
Here, i1=0 , . . . , 3k and i2=0, . . . 30-3k, whereby, “k” indicates the number of the corresponding TFCI1 bits (for example, if the ratio is 6:4, k=6).
In a 32 bit code word, j1 and j2 must have values between 0 and 31. However, the above bit position equations do not produce valid bit position for each TFCI ratio.
As such, the generation of these invalid bit positions creates errors in the TFCI code words generated therefrom. As a result, the reliability of DPCH or DSCH transmissions is undesirably decreased.